Swiss voters are set to back the government's plan to provide billions of dollars in subsidies for renewable energy, ban new nuclear plants and help bail out struggling utilities, broadcaster SRG projected.

The level of support in Sunday's referendum "will be above 55 per cent and thus far above any area of doubt," pollster Claude Longchamp said, basing the projection on partial results. 

Opinion polls had suggested the new energy law would be approved in the binding referendum, but support has slipped in the run-up to the vote. The Swiss initiative mirrors efforts elsewhere in Europe to reduce dependence on nuclear power, partly sparked by Japan's Fukushima disaster in 2011.

Germany aims to phase out nuclear power by 2022, while Austria banned it decades ago.

Referendums are common in Switzerland where voters get the final say on all major policy issues under a system of direct democracy.

Debate on the "Energy Strategy 2050" law has focused on what customers and taxpayers will pay for the measures and whether a four-fold rise in solar and wind power by 2035, as envisaged in the law, can deliver reliable supplies.

Critics have said a family of four would pay 3,200 Swiss francs ($3,290) in extra annual costs, while more intermittent wind and solar energy would mean a greater reliance on imported electricity.

Switzerland was a net power importer in 2016. Energy Minister Doris Leuthard dismissed such estimates as highly inflated.

She said the package would cost the average family 40 francs more a year, based on a higher grid surcharge to fund renewable subsidies.

Under the law, 480 million francs will be raised annually from electricity users to fund investment in wind, solar and hydro power.

An additional 450 million francs will be set aside from an existing fossil fuels tax to help cut energy use in buildings by 43 per cent by 2035 compared with 2000 levels.

Solar and wind now account for less than five percent of Switzerland's energy output, compared with 60 per cent for hydro and 35 percent for nuclear.

Under the new law, power from solar, wind, biomass and geothermal sources would rise to at least 11,400 gigawatt hours (GWh) by 2035 from 2,831 GWh now.

The law will ban building new nuclear plants.

Switzerland has five plants, with the first slated to close in 2019.

Voters have not set a firm deadline for the rest, allowing them to run as long as they meet safety standards.

Supporters say the law would also help utilities which now rely on hydropower, and whose costs exceed Europe's wholesale prices.

Alpiq, BKW, AXPO and other utilities would share a 120 million franc annual subsidy to help close the gap between production costs and market prices.

Other funds would help build new dams or refurbish old ones.

Source: Timesofoman